/Engine/Source/Editor/PlacementMode/Public/PlacementModeModule.h
Register a new placeable item for the specified category
Optional unique identifier for the registered item, or empty on failure (if the category doesn't exist)
virtual [TOptional](API\Runtime\Core\IO\TOptional)< [FPlacementModeID](API\Editor\PlacementMode\FPlacementModeID) > RegisterPlaceableItem ( [FName](API\Runtime\Core\UObject\FName) CategoryName, const [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [FPlaceableItem](API\Editor\PlacementMode\FPlaceableItem) > & Item )